Method of lamp manufacture



FIP8303 1-4 Jfx Patented Jan. 31, 1933 UNITED STATES litilli'tlililiilPATENT- OFFICE LLOYD D. LOCKWOOD,

OF MADISON, JERSEY, ASSIGNOR T0 WESTINGHOUSE LAMP COMPANY, A CORPORATIONOF PENNSYLVANIA METHOD OF LAMP No Drawing. Application filed .as thepresent invention.

It is one of the objects of this invention to provide an improved methodof manufacturing incandescent electric lamps of the evacuated type.

It is another object of vide a suitable getter material for centelectric lamps of the evacuated type.

It is another object of this invention to provide a getter material.useful in the manufacture of incandescent electric lamps of theevacuated type, which will effect substantial clean up of residualamounts of the relatively inert gases, such as nitrogen, and which willalso liberate within the device a proportion of readily vaporized highlyreactive material for the effective clean up of gases that may besubsequently evolved within the device from the filament and the surfaceof the enclosing glass envelope during the operating life of the lamp.

Other objects and advantages will become apparent as the invention ismore fully disclosed.

In copending application Serial No. 337,- 536 aboveid'entified, isdisclosed the use of a low temperature reducing flush gas comprisedsubstantially of an admixture of nitrogen,

this invention to pro- 1ncandes MANUFACTURE November 27', 1929. SerialNo. 410,259.

is beneficial in some manner to theluminous efficiency of the device.

In employing this type of reducing flush gas in the manufacture ofincandescent lamps and thermionic devices of the high vacuum type it isfound that even under the most rigid manufacturing control theevacuation of the device by mechanical exhaust methods is incomplete andthat residual amounts of the reducing flush gas remain within thedevice, and the usual type getter material heretofore employed does notsubstantially effect the removal thereof.

In copending application Serial No. 399,- 87 7 above identified, I havedisclosed a method of manufacturing incandescent lamps and electrondischarge devices of the high vacuo type employing the same type ofreducing flush gas set forth in application Serial No. 337,536, whereinthe residual gases remaining from the mechanical exhaust of the deviceare substantially removed by means of a getter material comprised atleast in part of a rare refractory metal powder which is reactive withsaid gases. It is contemplated in this second copending application thatthe getter composition employed should be comprised at least in part ofrare refractory metal powders and in particular, in part of zirconiummetal powder.

I have found that such a type getter material is particularly efl'ectivein cleaning up residual gases in evacuated electric devices, such asthermionic devices, fiers, X-ray tubes and the like, wherein it isundesirable to employ the readily vaporiz able highly reactive metalsmagnesium, aluminium, alkali, metal getters which have heretofore beenemployed in the art.

In incandescent electric lamps of the evacuated type it appears highlyessential and desirable that a proportion of getter material should bepresent within the device to react with deleterious impuritiesvolatilized from the incandesced filament or the heat enclosing glassenvelope during the operating life ofthe lamp. The use of the gettercomposition set forth in copending application Serial No. 399,877 aboveidentified, effects initially gas filled rectialkaline earth metals ormisch entitled a substantial clean up of the residual gases of theevacuated envelope and produces a marked improvement in the life andmaintenance of the lamp.

5 I have found, however, that it is inexpedient to incorporate thegetter material Within a getter helmet in a manner such as hasheretofore been employed in thermionic devices, radio tubes and thelike, which getter helmet is positioned with respect to the remainingparts of the lamp so that it is not substantially subjected to heatduring the manufacturing process. The getter composition, therefore, isapplied to the surface of the lamp filament in the customary mannerheretofore employed with the usual type cryolite-phos- ,phorus gettercomposition, as a result the getter material is subjected to the samedeleterious heating as has been heretofore expel rienced, and the rarerefractory metal compo nent thereof is at least in part oxidized orrendered inert to serve most eflicientl as a clean up agent whensubsequently ashed from the filament.

In copending application Serial No. 410,- 257 filed November 27, 1929,by Ewald Dietz', Getter for incandescent electric lamps is disclosed theuse of a metal phosphide, specifically copper phosphide, in the place ofthe usual phosphorus in the getter composition heretofore applied toincandescent lamp filaments.

The advantage obtained through the use of the metal phosphide in placeof phosphorus 35 in a getter composition is primarily that the metalphosphide compound is substantially stable at the elevated temperatures,customari ly employed in the baking out of the enclosing glass envelopeof an incandescent lamp during the sealing in and exhaust operations ofthe manufacturing process, and that they may subsequently be thermallydecomposed into their component elements, meta and phosphorus, byheating the phosphide to more elevated temperatures. In effect then, thephosphorus of the getter is fixed within the getter composition as aninert compound and subsequent to exhaust liberated within the device bythe thermal decomposition of the inert phosphide compound.

In the manufacture of incandescent electric lamps of the evacuated typeemploying the reducing flush" gas set forth in my copending applicationSerial No. 337,536, it is highly essential 'that not only should theresidual flush gas be cleaned up, but that a proportion of a gettermaterial should be evolved therein, which would be reactive withdeleterious gases and vapors evolved from the filament during subsequentincandescence or liberated from the enclosing glass envelope during theoperating life of the lamp.

It should be appreciated that under present day manufacturing conditionsthe fila- 65 ment of the lamp is not subjected to degasitype.

fication prior to sealing off as is customarily done with the metalparts of evacuated devices of the electron emitting or thermionicTherefore, there is evolved from the lamp filament a certain gas contentduring the operating life of the same, which gases are particularlydeleterious to the operating life and efficiency of the lamp.

In accordance with the objects of my invention, as above set forth, Ihave found that incandescent electric lamps of the evacuated type aresubstantially improved by subjecting the metal parts thereof to thesurface cleansing action of the reducing flush gas in accordance withthe invention set forth in copending application Serial No. 337,536above identified.

I have also found that the inert residual gases of an evacuated device,which has been flushed by this reducing flush gas, may be substantiallyremoved by incandescing therein a proportion of a rare refractory metalowder. I have also'found that it is essential for high operatingefficiency of the lamp to provide within the lamp a proportion ofphosphorus for the absorption of gases evolved during' the operatinglife of' the lamp from the incandescent filament and the enclosing glassenvelope. I have found that these three elements may be satisfactorilytaken care of by employing a getter material comprised of the usualinert constituent cryolite, sodium ferric fluoride or sodium aluminiumfluoride, in accordance with prior practice, to which has been added apropor' tion of a rare refractory metal phosphidecompound, such aszirconium phosphide, thorium phosphide, titanium phosphide and the like.

The specific rare metal phosphide compound may be made in accordancewith the process set forth in copending application Serial No. 410,245,filed November 27 1929, 1 by Wllliam C. Lilliendahl and Frank H.

Driggs, which application is assigned to the same assignee as thepresent invention.

In accordance with the practice of the present invention an incandescentelectric lamp of the evacuated type is subjected to the followingmanufacturing process.

The filament, either segmented or coil type, is, coated in the customarymanner with a getter composition comprised of cryolite containing a proortion of a rare refractory metal phosphide such as zirconium phosphide,titanium hosphide or thorium phosphide, in a su cient proportion to givefrom .3% to 40% phosphorus, the specific proportion thereof depending'upon the particular size and shape'of the enclosing glass envelope ofthe lamp. Owing to the difiiculty of maintaining dip or spray gettercompositions free of moisture, organic suspension medium, such asamylacetate, alcohol, diethyl carbonate and the like solvents withinwhich is dissolved a proportion of 130 LUZ-u nitrocellulose binder, areunsatisfactory for general purpose use, as the moisture tends to reactwith the metal phosphide forming various undesirable decompositionproducts. I prefer, therefore, to use the dry getter method of getteringfilaments such as is set forth and disclosed in copending applicationSerial No. 277,106, filed May 11, 1928 by D. S, Gustin, whichapplication is assigned to the same assignee as the present invention.The gettered filament is then mounted in the usual manner andincorporated within an enclosing glass envelope by the customary sealingin operation. i

The device is then exhausted by mechanical exhaust means and theenclosing glass envelope subjected during the exhaust operation to abaking temperature of from 375 to 600 C. depending upon the particularcomposition of the enclosing glass envelope. When a fair degree ofvacuum has been obtained the device is then flushed with the lowtemperature reducing gas as set forth in my copending applicationsSerial No. 375,536 and No. 399,877 above identified, and the metal partsof the lamp cleansed of surface impurities. The reducing flush gas isthen removed by the mechanical exhaust means and the evacuated devicesealed off without .permitting the cleansed metal parts to becomeexposed to deleterious atmospheric gaseous absorption.

After sealing off the lamp the filament is incandesced and the zirconiumphosphide component of the getter, for example, is vaporized andthermally decomposed. The highly reactive zirconium metal componentliberated thereby effectually cleans up the residual nitrogen, hydrogenand oxygen of the device and the liberated phosphorus com ponent remainsavailable within the envelope to clean up the oxygen or moisture evolvedduring the incandescing life of the device from the incandescentfilament or from the enclosing walls of the glass envelope or producedtherein by reason of certain cyclic reactions heretofore identified inthe art.

As a result of the practice of the present invention a material increasein the life and maintenance of incandescent electric lamps is obtained,due it is believed to the eliminating, by use of the reducing flush gas,of

. surface metal oxide impurities which subsequently deleteriously effectthe operating efficiency of the device by interaction with theliberated. hydrogen of the incandescent fila ment.

.It is also believed the material increase in life and maintenance isdue in large part to the fact that the getter material upondecomposition is comprised in part of a component which is specificallyreactive with the substantially inert residual gases of the evacuateddevice and in part of a vaporizable component which is highly reactiveto residuse ual gases which may be evolved subsequent to the initialclean up of the device during operation of the same. This combination ofbeneficial effects produces a uniformity in lamp quality 7 notheretofore obtainable in lamp manufacture.

From the above description it is apparent that there may be manyvariations and departures from the specific embodiment herein disclosedwithout substantially departing from the nature of the present inventionas set forth in the following claims:

What is claimed is:

1. The method of cleaning up residual gases in an incandescent electriclamp which comprises thermally decomposing a rare refractory metalphosphide.

2. The method of cleaning up residual gases in an incandescent electriclamp which comprises thermally decomposing zirconium phosphide.

3. The 1 method of cleaning up residual gases in an incandescentelectric lamp which comprises vaporizing therein a proportion of a rarerefractory metal phosphide.

4. The method of cleaning up residual gases in an incandescent electriclamp which comprises vaporizing therein a proportion of zirconiumphosphide.

5. In the manufacture of evacuated incandescent electric lamps, thesteps of effecting substantial removal of residual gases which comprisesthermally decomposing a proportion of a rare refractory metal phosphidecompound.

6. In the manufacture of evacuated incandescent electric lamps, the stepof effecting substantial removal of residual gases which comprisesthermally decomposing a proportion of zirconium phosphide.

7. The methodof manufacturing incandescent electric' lamps of theevacuated type which comprises incorporating within the device a gettercomposition comprised at least in part of a proportion of ararerefractory metal phosphide compound, evacuating the device, flushingthe evacuated device, evacuating the flush gas, sealing off the device,and then thermally decomposing tory metal phosphide component of thegetter.

8. The method of manufacturing incandescent electric lamps. of theevacuated type which comprises"incorporating within the device a gettercomposition comprised at least in .part of a "proportion of a rarerefractory metal phosphide compound, evacuating the device, baking thedevice, flushing the device'during baking with a low temperaturereduoingflush gas, evacuating said fiush gas, sealing off the device,and then thermally decomposing the rare refractory metal phosphidecomponent of the getter.

9. The method of manufacturing incandescent electric lamps of theevacuated type the rare refracwhich comprises incorporating within thedevice agetter composition comprised at least in part of a proportion ofa rare refractory metal phosphide compound, evacuating the device,flushing the device with water gas while maintaining the metal parts ofthe device at temperatures approximating 37 5 CL to 450 C. evacuatingthe flush gas, sealing off the device, and then effecting thermaldecomposition of the rare refractory metal component of the gettercomposition.

10. The method of manufacturing incandescent electric lamps of theevacuated type which comprises incorporating within the device a gettercomposition comprised at least in part of zirconium phosphide,evacuating the device, flushing the device with a low temperaturereducing flush gas comprised of nitrogen, carbon monoxide and aproportion of hydrogen, maintaining the metal parts of the device duringthe flushing operation at temperatures approximating 37 5 C. to 450 C.evacuating the flush gas, vice, and then efiecting clean up of residualgases within the device by the thermal decomposition of the zirconiumphosphide component of the getter.

11. The method of manufacturing incandescent electric lamps of theevacuated type which comprises applying to the filament prior toincorporation within the lamp 2, getter composition comprised at leastin part of a rare refractory metal phosphide compound, incorporating thegettered filament into a lamp, evacuating the device, cleansing themetal parts with a water gas reducing flush gas, evacuating the flushgas, sealing off the device and then cleaning up the residual gases inthe device by effecting a'vaporization and decomposition of the rarerefractory metal component of the getter composition.

12. The method of manufacturing incandescent electric lamps of theevacuated type which comprises applying to the filament prior toincorporation into the lamp a getter composition comprised at least inpart of zirconium phosphide, incorporating the gettered filament into alamp, evacuating the device, cleansing the metal gas reducing flush gas,evacuating the flush gas, sealing ofi the device and then cleaning upthe residual gases in'the device by effecting a vaporization anddecomposition of the rare refractory metal component of the gettercomposition.

13. An evacuated device containing a getter composition comprised atleast in part of a rare refractory metal phosphide.

14. An evacuated device comprising a getter composition comprised atleast in part of zirconium phosphide.

15. A getter composition for evacuated incandescent electric lampscomprised of an inert material vaporizable at a temperature parts with awater above 600 C. and a proportion of rare refractory metal phosphide.

16. A getter composition for evacuated incandescent electric lampscomprised of an inert material vaporizable at a temperature above 600 C.and a proportion of zirconium phosphide.

17. A getter composition for evacuated incandescent electric lampscomprised of cryolite and a proportion of rare refractory v metalphosphide.

18. A getter composition for evacuated incandescent electric lampscomprised of cryolite and a proportion of zirconium phosphide.

In testimony whereof, I have hereunto subscribed my name this 25th dayof November, 1929.

LLOYD D. LOCKWOOD.

sealing off the de-

